A perpendicular recording system using media with a soft underlayer has the advantage of providing a larger write field than systems without such underlayer. With a soft underlayer, magnetic flux travels from the main writing pole 11 into underlayer 12 and back through return pole 13, as symbolized by solid lines 14 in FIG. 1. The flux that returns via the underlayer also passes through the recording layer, but at a lower density than the write field because of the greater width of the return pole relative to the write pole.
However, if the flux that passes through the return pole is strong enough, it can still erase previously recorded data since the return flux includes not only flux emitted from the tip of the main writing pole, but also flux leaked from yoke 16, shown as dotted line 15 in FIG. 1. The contribution to the density of return flux from this source can be significant because the size of the disk is far larger than the head so most of leaked flux would be collected and then concentrated at the return pole.
Also shown in FIG. 1 is write coil 17 that surrounds yoke 16.
In a prior application (No. 09/942,290) it was shown that when a pole head is driven differentially, the return pole field is greatly reduced. Here we disclose a design that uses the conventional single coil.
A routine search of the prior art was performed with the following references of interest being found:
U.S. 2002/0176214 (Shukh et al) and 2002/0141111 and 2002/0071208 (Batra et al) all show a main pole between two return poles. In U.S. Pat. No. 4,380,768, Palumbo et al. disclose a single protrusion forming a recording head and all the surrounding protrusions forming the return pole while Sherrer et al. describe a U-shaped return pole in U.S. Pat. No. 6,501,619.
Hore (in U.S. Pat. No. 5,214,378) shows a displacement sensor having two pairs of active poles and two return poles. In U.S. Pat. No. 4,317,148, Chi discloses a single recording pole and a flux return pole while Batra teaches a single return pole and a main pole in U.S. Pat. No. 6,574,072.